Because of the unique set of properties of polyolefins such as polybutylene and polypropylene, particularly their high compliance compared to other polyolefins and their comparatively low melting temperature, a functionalized version becomes an excellent candidate to fill the requirements of a structural hot melt adhesive. Polybutylene without functional groups lacks the functionality or polarity needed for the adhesion to high surface energy substrates, a necessary characteristic for both hot melt adhesives and their constituents.
Polybutylene, like other polyolefins, has no functionality on the chain and therefore artifacts made from this polymer have very low surface free energy and can not be decorated by painting or printing. In the past, researchers have reacted functional groups on the surface of polyolefins by various means using highly oxidative techniques to induce bonding sites with reagents leaving hydroxyl or carboxyl groups. Also, melt reactions have been carried out to functionalize the bulk of the polyolefin material by a free radical initiated reaction induced by organic peroxides.
A large number of polymer companies commercially offer functionalized polyolefin materials such as acrylated and maleated polypropylene and polyethylene. Techniques used to modify these polymers provide one or, at most, two acid groups per grafting site. The present inventor has found that by increasing the number of functional groups to three or greater per grafting site one can substantially improve the polarity and hence improve the polymer's performance in several end use application.
Additionally, there is an ever increasing impetus to replace or supplement solvent-based polymer coating compositions with aqueous-based counterparts due to the environmental toxicity and flammability problems posed by the use of volatile organic solvents. However, even where aqueous-based polymer compositions have been devised, their production has usually entailed the intermediate use of organic solvents, requiring subsequent removal which is costly and time-consuming, or the incorporation of a certain amount of a solvent in the final composition which acts to ensure proper film-formation on coating (known as a coalescing solvent). There is therefore also now increasing pressure to significantly reduce or eliminate the volatile organic contents (VOCs) in aqueous-based polymer composition syntheses both as components in their production (even if subsequently removed) and in the resulting composition as an aid to film coalescence.
In the present invention, applicants have found unexpectedly that multi-carboxylic acid as the functional group can co-ordinate very effectively with most metals to form stable, e.g. octahedral, anionic complexes. For example, two moles of iminodiacetic acid contain four carboxylic acid groups, which can react with metal ions to form to have stability constant in excess of 10.sup.10. The introduction of carboxylic functionality into polyolefins allow for more water solubility as well as production of water borne products which are environmentally desirable.